Optical print head with LED diode array

ABSTRACT

An optical printer includes an optical printing head and a photosensitive member. Although quiet and fine printing can be performed when a light emitting diode array is employed as the optical printing head, there have been problems, on the other hand, such as difficulty in driving and difficulty in adjustment of primary factors directly affecting the printing quality such as uneveness in dot pitches and intensity. Therefore, the present invention copes with driving conditions by effectively distributing data transferring during static driving, thereby to improve the printing quality by selective printing timings.

FIELD OF THE INVENTION

The present invention relates to an optical printing head to be employedin an optical printer which reflects aligned dot-shaped optical imageson a photosensitive member for printing the same. More specifically, itrelates to an optical printing head which comprises light emitting diodearrays and means for driving the same as the optical printing head.

BACKGROUND OF THE INVENTION

Recently, in a computer terminal device, a plain paper copyingapparatus, a picture record printer and the like, optical printersutilizing a combination of fine light emitting points and photosensitivemembers have been developed with attention directed to advantagesthereof such as high-speed, high resolution, fineness in printing andquietness of the devices. Such devices are called as a laser printer, alight emitting diode printer (LED printer) and the like depending ontypes of light sources employed therein.

LED printers according to the prior art of interest are disclosed inU.S. Pat. Nos. 3,850,517 (Stephany et al.), 4,318,597 (Kotani et al.)and Japanese patent laying-open gazette No. 55770/1984 (Yoshida) etc.These are now briefly described with attention to optical printing headsand driving methods.

First, the LED printer disclosed in U.S. Pat. No. 3,850,517 has adecoder in each block of light emitting diode arrays and employs codesas printing data. Therefore, although the transfer speed of the printingdata itself is high, a number of decoders and printing timings afterdecoding of the printing data are required, and further, this printercannot be applied to printing of those not included in characters, e.g.,picture images.

Next, the LED printer disclosed in U.S. Pat. No. 4,318,597 compriseslight emitting diode arrays alternately arranged in the so-calledzig-zag manner and printing data are formed by serially transferred dotinformation, and hence it is suitable for printing of picture images andthe like. However, the data are basically transmitted to shift registersin a series manner, and one of the arrays is delayed by a memory incompliance with the zig-zag arrangement. Consequently, this LED printerrequires a long data transfer time, and further requires two systems ofprinting timings synchronized with the cross scanning direction.

Lastly, the LED printer disclosed in Japanese patent laying-open gazetteNo. 55770/1984 is of a typical dynamic lighting type, and hence commonelectrodes are separated for each of light emitting diode arrays and anumber of timing signals for light emitting points are required withrespect to a horizontal scanning line.

A light emitting diode array is provided with light emitting areas(dots) being in alignment, which correspond in size and position to dotsto be printed in the 1:1 ratio. On the other hand, one light emittingdiode cannot form all dots over the entire length of the main scanningdirection, and hence a plurality of short light emitting diode arraysare employed in alignment. Therefore, dot pitches are required to beconstant in joints of the light emitting diode arrays. However, when therespective ones of the light emitting diode arrays are placed onseparate substrates to be arranged in two lines as in the aforementionedmaterials, alignment of the optical images (i.e., supporting of thelight emitting diode arrays and adjustment of the optical systems) isextremely difficult. Further, connection of common line independentlyprovided for each of the light emitting diodes for dynamic drivingcomplicates operation for the alignment is complicated. Placing aplurality of light emitting diode arrays on one substrate without regardto the connection of common line would be a method of solving theproblem of difficulty in such work. More preferably, the plurality oflight emitting diode arrays are arranged in one line.

Further, an LED printer has such an advantage that a head thereof is asolid element which enables high-speed printing, wherefore high-speeddata processing is required. However, if extreme high-speed is requiredfor the data transfer speed and the transfer time is lengthened, thesaid advantage cannot be efficiently applied while integrated circuitelements to be used are restricted, and the power consumption isincreased in case of, e.g., a high speed TTL, leading to inconvenience.

In addition, intensity of the head shows dispersion depending on thesynergistic effect of the light emitting characteristics of the lightemitting diode arrays and the output characteristics of drivingelements, whereas no definite countermeasures therefor are indicated inthe aforementioned prior art examples. The present invention has beenproposed in consideration of these points.

DISCLOSURE OF THE INVENTION

Accordingly, a primary object of the present invention is to provide anoptical printing head which can print bit-unit serial printing datareceived therein at a high speed. According to the present invention,lowered is the shifting speed for shifting the serial printing data tocorrespond to positions of light emitting areas (dots) in the head.Consequently, an integrated circuit of a MOS (Metal Oxide Semiconductor)type which is a low-power consumption element can be used thereby tolower the power consumption of the optical printing head. In order tofacilitate assembling of light emitting diode arrays, one side of eachdiode is connected as a common electrode, thereby to enable one-linealignment of dots.

Another feature of the present invention resides in that brightnesscontrol is performed in conformity to characteristics upon combinationof light emitting diodes and driving elements.

The present invention is characterized in that light emitting areas(dots) of light emitting diode arrays are separated into a plurality ofgroups so that adjacent ones belong to groups different from each other,and serial printing data are divided and transferred per each group.Preferably, anodes or cathodes of the light emitting diode arrays arecommonly connected.

By virtue of this, the shifting speed of shift registers used for serialtransferring in an optical printing head in practice is 1/(number ofgroups) of the serial printing data as transmitted, and common sideseparation which prevents placing in alignment in one straight line maynot be performed.

Further, in the present invention, a printing timing in response tolight emission intensity is supplied to each of specified blocks, andpreferably wiring is selectively performed for each block from aplurality of printing timings. Consequently, the present invention canselectively obtain printing timings for making light emission intensityconstant after arrangement and wiring of elements.

Other objects and features of the present invention will be moreapparent from the detailed description hereafter made with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an optical printing headaccording to the present invention.

FIG. 2 is a plan view of an essential part of a substrate employed forthe optical printing head (however, wire bonding thin lines for wiringare omitted).

FIG. 3 is a perspective view of a light emitting diode array similarlyemployed for the substrate.

FIG. 4 is a typical wiring diagram of the substrate as shown in FIG. 3.

FIG. 5 is a circuit diagram of an essential part of an optical printinghead according to an embodiment of the present invention.

FIG. 6 is a timing chart of FIG. 5.

FIG. 7 is a frequency-power consumption characteristic diagram ofvarious types of driving elements.

FIGS. 8 and 9 are equivalent circuit diagrams of driving elementsaccording to other embodiments of the present invention.

FIG. 10 is a circuit diagram of signal distribution means according toanother embodiment of the present invention.

BEST MODES OF CARRYING OUT THE INVENTION

Density of light emitting areas (dots) of a light emitting diode array(hereinafter referred to as LED) employed in an optical printing headsubstantially corresponds to printing dot density, which density isabout 9 dot/mm to 20 dot/mm or over, and a monolithic type LED isemployed. There is a limitation in lengthening of an LED in relation tothe size of a wafer and yield, and hence the size of an LED is made tobe about 6 to 10 mm in length, and the same is utilized in arrangementin lines.

FIG. 1 is an exploded perspective view of an optical printing heademploying such LED, in which LEDs (2) (2) . . . are arranged on asubstantially central portion of a substrate (1) of ceramics etc. havingpatterns, and driving elements (3) (3) . . . are arranged on both sidesthereof. This substrate (1) is stacked on a heat sink (4) to be coveredby a frame member (6) having a glass member (5). A metal frame member(7) contains these components and is fixed to the heat sink (4). Aconductive path (not shown) for the substrate (1) is electrically drawnout to the exterior from a hole (7') provided in the heat sink (4)utilizing an auxiliary substrate (8) and a connector (9).

FIG. 2 is a plan view of an essential part of the substrate (1), inwhich the LEDs (2) (2) . . . are arranged in alignment on a strip-shapedconductor (11) provided in the center. With respect to the LEDs (2) (2). . . , as shown in FIG. 3, a GaAsP graded layer (22) gradually changingfrom the substrate side from GaAs to GaAs₀.6 P₀.4 and a GaAs₀.6 P₀.4layer (23) are grown in a vapor epitaxial manner on an n-type GaAssubstrate (21), and light emitting areas (24) (24) . . . are formed byselective diffusion by p-type impurities. Electrodes (25) and (25) forthe light emitting areas (24) (24) . . . are longitudinally provided inan alternate manner by aluminum etc. Further, a common electrode (26) ofa gold alloy etc. is formed on the back surface of the GaAs substrate(21). The mixed crystal ratio of GaAs and GaP in the GaAs₀.6 P₀.4 layer(23) is selected in conformity to the photosensitive characteristics ofa photosensitive member (not shown) such that, e.g., an amorphoussilicon photosensitive member has the maximum sensitivity of 660 nm andhence the mixed crystal ratio is made 0.6, i.e., GaAs₀.6 P₀.4. Indefinite exemplification with respect to the LED (2), it has 96 dots ofsquare-shaped light emitting areas (24) (24). . . each in size of 1 mm×8mm and having a side of 50 μm in a pitch P₁ =84.5 μm, thereby to haveresolution of 12 dot/mm. In case of a head for an A4 size, the effectiverecording length (horizontal scanning length) thereof is 216 mm andhence 27 LEDs are arranged in alignment while evenly retaining the dotpitches. These LEDs (2) (2) . . . are placed on and fixed to theaforementioned strip-shaped conductor (11) by a conductive bonding agentetc., whereby all of the light emitting areas (24) (24) . . . are soconnected that the n-sides are in common. The driving elements (3) (3) .. . arranged on both sides of the LEDs (2) (2) . . . contain shiftregisters and LED drivers, and, as hereinafter described in detail, areso wired that those positioned over the light emitting areas drive evennumber light emitting areas and those positioned under the same driveuneven number light emitting areas respectively in a separate manner, asshown in FIG. 4. Wiring of the same is performed by conductive patterns(12) (12) . . . on the substrate (1) and wire bonding thin lines (notshown) with respect to the same. Three conductive patterns (13a), (13b)and (13c) provided in parallel to the array of the LEDs (2) (2) . . .are duty lines for brightness control, which are also hereinafterdescribed in detail.

FIG. 5 is a circuit diagram of an essential part of the optical printinghead according to the embodiment of the present invention, in whichdiodes (20) (20) . . . correspond to the light emitting areas (24) (24). . . and the LEDs (2) (2) . . . have common cathodes as hereinabovedescribed, which are connected to the minus side (V⁻ or groundpotential) of a driving power source. On the other hand, the drivingelements (3) (3) . . . are formed by MOS-type LSI, and have shiftregisters (31) (31) . . . in a bit number (N/2 bits) corresponding to1/2 of a number N (N=96 in the aforementioned example) of the diodes(20) (20) . . . for one LED (2) and latch circuits (32) (32) . . . ofN/2 bits, as well as N/2 of AND gates (33) (33) . . . and drivertransistors (34) (34) . . . However, the latch circuits (32) (32) . . .can be omitted when timing control of lighting timing signals and datatransfer clocks can be effectively performed. Further, the drivertransistors (34) (34) . . . may also be omitted when the currentcapacity of output stages of the AND gates (33) (33) . . . issufficient. In a MOS-type transistor, limitation in current capacity isoften significant and generally a bipolar transistor array has beenseparately prepared especially in case of a C-MOS transistor. However,with a driving current for driving the dots by one driver being no morethan 15 mA, P-channel open drain MOS transistors can be employed as thedriver transistors (34) (34) . . . as shown in the drawing, whereby thedriving element (3) can be one-chip monolithized. The sources of thedriver transistors (34) (34) . . . are commonly connected to an LEDlighting power source (V⁺), and the drain sides are respectivelyconnected to only odd number ones or even number ones of the diodes (20)(20) . . . per driving element successively. In other words, if thenumber of the diodes over the entire length is, e.g., 2592, they arenumbered from one end as 1, 2, 3, . . . , 2952, to be separated intodriving elements directed to odd number ones of 1, 3, 5, 7 . . . anddriving elements directed to even number ones of 2, 4, 6, 8 . . . (referto FIG. 4). Therefore, the shift registers (31) and (31) are separatedinto two systems of those storing lighting control data of even numberlight emitting areas (24) (24) . . . and those storing lighting controldata of odd number light emitting areas (24) (24) . . . , which areconnected in series in the respective systems.

Numerals (41), (42) and (42) indicate a toggle-type flip-flop and ANDgates forming signal distribution means for distributing seriallytransferred bit-unit printing data (D) in the shift registers (31) (31). . . of the two systems of odd and even numbers and outputting thesame. These are adapted to alternately open and close the AND gates (42)and (42) per one pulse of data transfer clocks (φ) and alternately allowpassage of printing data signals, thereby to successively distribute theprinting data in the aforementioned two systems. Further, output signals(CL₁) and (CL₂) of the flip-flop (41) are respectively utilized asclocks for data transferring of the shift registers (31) (31) . . . ofthe respective aforementioned two systems as they are.

Numerals (51) (52) (53) and (54) (54) (54) indicate a trigger circuit(51), an AND gate (52), a counter (53) and set-reset type flip-flops(54), (54) and (54) for producing signals (T₇₀), (T₈₀) and (T₉₀) of theduties of 70%, 80% and 90% of lighting timing based on lighting timingsignals (T). Namely, the counter (53) receives the lighting timingsignals (T) to count the data transfer clocks (φ), and successivelyoutputs counter outputs when the clock numbers reach those correspondingto 7/10, 8/10 and 9/10 of a lighting timing period (e.g., clock). Theflip-flops (54), (54) and (54) receive the rise of the timing signals(T) to be set, and receive outputs (7 clocks, 8 clocks and 9 clocks) ofthe counter (53) to be reset. Therefore, the outputs are obtained duringthat period, to become a 70% duty signal (T₇₀), an 80% s of theseflip-flops (54), (54) and (54) determine substantial lighting times ofthe diodes (20) (20) . . . , and hence they are provided on thesubstrate (1) in patterns in parallel with the direction of alignment ofthe LEDs (2) (2) . . . , i.e., as the aforementioned duty lines (13a),(13b) and (13c) so that any output line can be selected per element.

These signal distribution means (the flip-flop (41) and the gates (42)and (42)) and intensity control timing means (the trigger circuit (51),the gate (52), the counter (53) and the flip-flops (54), (54) and (54))are preferably formed by high-speed bipolar transistor logics which arehigh-speed and excellent in output stability, in the exterior of thesubstrate (1).

FIG. 6 is a timing chart of an essential part of FIG. 5. The printingdata (D) are transmitted by serial transfer of information H and L onlighting and unlighting of the diodes (20) (20) . . . in synchronizationwith the data transfer clocks (φ) from, e.g., a picture memory, acommunication bus or a character code decoder (all not shown).Therefore, the flip-flop (41) forms data transfer clocks (CL₁) and (CL₂)and the data (D) are guided to the AND gates (42) and (42) thereby toproduce uneven number data (D₁) and even number data (D₂ 2) synchronizedwith the same. Thus, the data can be transferred in the same time asrequired for transferring original series data, and further, theshifting speed in each of the shift registers (31) (31) . . . is 1/2 ofthe transfer speed of the serial data.

This is extremely important. FIG. 7 shows a relation between inputfrequencies and gate power consumption by types of elements, and a lowpower consumption of a MOS (C-MOS) transistor is obtained when the sameis driven at a low voltage, and the response speed is slow at this time.This is because a dynamic power consumption (P) of the C-MOS transistorhas the following relation with respect to the input pulse frequency(f), the load capacity (C_(L)) and the power supply voltage (V_(DD)):

    P=F·C.sub.L ·V.sub.DD.sup.2

It is to be noted that this relation is one with respect to the basicC-MOS unit, and not all of the logics are simultaneously switch-operatedwhen integrated in high density, and a number of gates operatesubstantially at inner lower clocks and hence the power consumption isless than that in FIG. 7. However, the power consumption can becontrolled at a low value slow as the operation speed (data transferspeed) may be, thereby to make effective use of the MOS transistor whichis characterized in a low power consumption.

The timing signal (T) for lighting is supplied upon completion oftransferring of the printing data (D), and hence the latch circuits (32)(32) . . . are latched by an output (T') of the trigger circuit (51)responding to the rise thereof to fetch parallel output data of theshift registers (31) (31) . . . and output the same thereby to retainthe outputs. Since the AND gates (33) (33) . . . perform the high leveloutputs when the inputting conditions are satisfied, the drivertransistors (34) (34) . . . are turned on and the diodes (20) (20) . . .selectively emit lights. When the same lighting timing signals aresupplied in the odd number side and the even number side, the selectedones of the diodes (20) (20) . . . are simultaneously lighted withoutregard to the odd and even numbers. If the lighting timing time has asufficient margin, the lighting timing can be divided in two forperforming time-sharing lighting with the first half in the odd numbersand the latter half in the even numbers. The data of the latch circuits(32) (32) . . . are changed only when there are latch signals, and hencedata transferring of the next line can be performed during the lighting.

In definite exemplification, in an optical printing head of A4-sizeresolution of 12 dot/mm and the horizontal scanning dot number of 2592dots, the data transfer time was about 1.04 msec (2.1 msec in seriesconnection of all of conventional shift registers) with driving at 5 Vand a data transfer clock (φ) of 1.25 MHz, and when the lighting currentper dot was 10 mA, the power consumption of the optical printing head inlighting of all dots (lighting duty cycle of 0.40) was 5.1 W.

At least one of input signals of the AND gates (33) (33) . . . of thedriving elements (3) (3) . . . is commonly connected per each of thedriving elements (3) (3) . . . to be terminal-extracted as dimmer lines(35) (35) . . . The dimmer lines (35) (35) . . . are selectivelyconnected to one of the output lines (T₇₀), (T₈₀) and (T₉₀) of theflip-flops (54), (54) and (54), i.e., the duty lines (13a) (13b) and(13c) by a wire bonding method similarly to other wires.

In assembling of the optical printing head, the LEDs (2) (2) . . . andthe driving elements (3) (3) . . . are placed on and fixed to thesubstrate (1), and wiring is performed except for the dimmer lines (35)(35) . . . The dimmer lines (35) (35) . . . are connected by tentativeconnection with lighting timing signal (T) lines to perform fulllighting (either of simultaneous driving and sequential driving will do)thereby to find the average intensity of the light emitting areas (24)(24) . . . For example, when intensity dispersion of a single unit ofthe LEDs (2) (2) . . . is 8% and output characteristic dispersion of thedriving elements (3) (3) . . . is 18%, the values are substantiallywithin ±14% with respect to desired values as a whole. And if theaforementioned average intensity is ±5% desired value, the dimmer lines(35) are connected to the output line (T₈₀) (13b) of the 80% duty, andin a similar manner, connected to the output line (T₇₀) (13a) of the 70%duty when the same is +5.1 to +14% (brighter by about 10%) and connectedto the output line (T₉₀) (13c) of the 90% duty when the same is -5.1 to-14% (darker by about 10%) respectively in a selective manner. Thus, thewhole intensity dispersion is substantially within ±5%, and henceuneveness in printing density of the LED printer cannot be visuallyrecognized when light emitting peak wavelength of the LEDs (2) (2) . . .is matched with the photosensitive characteristics of the photosensitivemember.

FIGS. 8 and 9 show driving elements (3) which are provided in outputstages thereof with means for minimizing intensity dispersion, therebyto prevent characteristic dispersion of diodes (20) (20) . . . of singleLEDs (2). In FIG. 8, resistors (36) (36) . . . are connected in seriesto drains of driver transistors (34) (34) . . . , while constant currentelements (37) (37) . . . are connected in a similar manner thereto inFIG. 9. The resistors (36) (36) . . . are formed by structure equal to,e.g., a diffused resistor or a MOS channel transistor, and the intensitycan be made uniform as the resistance value is increased. However, ifthe driving current for the diode (20) is made constant in order toobtain prescribed intensity, the power consumption is more increased incase of a higher resistance value and it is difficult to manufacture onehaving a high resistance value by application of MOS technique. Thus,the resistance value is preferably 250 to 300 Ω. On the other hand, theconstant current elements (37) (37) . . . are formed by self-bias ofjunction type FET, which FET can be formed by diffusion and evaporationof aluminum electrodes, although the same cannot be manufactured byexactly the same steps as those of MOS circuits of other shift registersetc. Further, when fine adjustment is required in these means, the samemay be performed by trimming by etching or by laser light beams in caseof the resistors and by supplying connecting lines between gates anddrains with resistance components in case of the FET.

FIG. 10 is a circuit diagram of a signal distribution means in anotherembodiment of the present invention. Although the light emitting areas(diodes) are separated into an odd number group and an even numbergroup, i.e., into groups 2i-1 and 2i (i indicates a natural number) inthe aforementioned embodiment, when the same are separated into m groupsso that adjacent light emitting areas (diodes) belong to separategroups, the shifting speed of the data in the respective shift registerscan be slowed by the group number m, i.e., to the speed 1/m of theserial data transfer speed. In contrast with this, when the shiftingspeed of the data in the shift registers may not be slowed so much, theserial data transfer speed can be increased, thereby to cope with asuperhigh-speed printer. FIG. 10 shows signal distribution means of data(D) when light emitting areas (diodes) are divided into m groups.Employed are m-bit shift registers (43) so that data of the shiftregisters (43) are produced by a flip-flop (44) which is set at a finalbit and reset at the initial bit, thereby to produce 1/m-divided clocksof data transfer clocks (φ). Namely, respective outputs of the shiftregisters (43) are deviated by one data transfer clock from each other,so that the frequency becomes a pulse train of 1/m of the data transferclock. By AND of the output of the shift register (43) and the data (D),mi-(m-1), mi-(m-2), . . . , mi (i indicates a natural number) order dataare distributed by m AND gates (45) (45) . . . substantially supplyinggates for the data. An OR gate (46) is provided for setting theflip-flop (44) by an initial data flag (I) which supplies a first clocktiming to be distributed. Although such is not shown, light emittingareas of LEDs must also be divided into m groups so that light emittingareas to be printed with respect to the same belong to groups to beprinted, to be coped with m-groups of shift registers which areconnected in series per group. Further, if transfer clocks are requiredfor the shift registers, the output signals of the shift register (43)may be utilized.

POSSIBILITY OF INDUSTRIAL UTILIZATION

The optical printing head according to the present invention receivesdot information transferred in a high-speed serial manner as inputs, andhence it can be applied to optical printers for printing characters andpicture images etc. such as a copying apparatus, a facsimilecommunication system and a computer terminal. Since data transferring isperformed at a low speed in a parallel manner in the head, the presentinvention is extremely effective in high-speed high-resolution printing.Further, a MOS-type integrated circuit can be utilized by lowering ofthe transfer speed in the head and the light source is a solid statesemiconductor, whereby an extremely quiet optical printing head can besupplied at a low power consumption. Still further, since intensitybalance in the light source is adjusted by pairs of driving elements andlight emitting diode arrays, the optical printing head can be easilymanufactured with printing qualities (printing points and printingdensity made constant) being extremely excellent. In addition, the dotscan be single-arrayed and hence the optical printing head can be easilyhandled, and further, adjustment with surrounding optical systems (forexample, a short-focus lens array and a photosensitive member) wherebythe present invention also contributes to simplicity in manufacturing ofthe optical printer itself and readiness in maintenance thereof.

We claim:
 1. An optical printing head for an optical printercomprising:(i) a plurality of light emitting diode arrays having amultiplicity of aligned light emitting areas arranged substantially in aline, with one feeding path for each of said light emitting areas beingsubstantially commonly connected, and the other feeding path for saidlight emitting areas being divided into a plurality of m groups, wherem≧2, so that adjacent light emitting areas belong to groups differentfrom each other, (ii) means for storing printing data provided for therespective ones of said groups with respect to said other feeding pathfor light emitting areas of said plurality of light emitting diodearrays, including shift registers for transferring the printing data anddriving means for supplying current to said light emitting areas bymeans of the data from said shift registers, (iii) data distributionmeans coupled to said shift registers for distributing a series ofprinting data of one dot line via serial transfer at a predeterminedspeed in said shift registers for the respective ones of said groups, ata shifting speed of 1/m of said serial transfer speed, and (iv) drivingtiming means for outputting data simultaneously for the respective onesof said means for storing data from said shift registers to said drivingmeans, and driving said driving means in a static manner for the lightemitting areas of one dot line to simultaneously and selectively emitlight from said light emitting areas.
 2. An optical printing head inaccordance with claim 1, wherein group division of said light emittingareas is so performed that they are divided in two, into a group of oddnumber ones and a group of even numbers of said light emitting areas inorder of alignment.
 3. An optical printing head in accordance with claim1, whereinsaid means for storing said printing data is formed by aMOS-type integrated circuit.
 4. An optical printing head in accordancewith claim 1, whereinsaid driving means includes a plurality of printingtiming means selective in response to light emission intensity.
 5. Anoptical printing head in accordance with claim 3, whereinsaid drivingmeans is also formed integrally with said means for storing saidprinting data and comprises driving power stabilizing means for saidlight emitting areas.
 6. An optical printing head in accordance withclaim 4, whereinsaid printing timing means include duty lines fortransmitting lighting timings different in duty ratio from each otherwith respect to printing periods.
 7. An optical printing head inaccordance with claim 6, whereinsaid duty lines longitudinally extendsubstantially in parallel with the extending direction of said lightemitting diode arrays.
 8. An optical printing head in accordance withclaim 1, whereinsaid light emitting diode arrays are placed on and fixedto a strip-shaped conductor in a line.